Nitrogen Use Efficiency in Kentucky Bluegrass.

Nitrogen (N) is generally the most limiting nutrient in turfgrass soils. Shallow rooting and typical over application of irrigation water and fertilizer frequently result in N availability fluctuations with negative impacts on shoot and root growth, color, stability, and nutrient pollution. Inherent inefficiencies in N uptake result in nutrient pollution in the atmosphere and in water supplies. A controlled-release N fertilizer, in the form of polymer-coated urea (PCU), is a possible alternative to traditional N sources. A newly formulated PCU has been shown to meet plant demand in a timely and efficient manner through temperature-controlled release of N into the soil solution. This PCU may also decrease nitrous oxide (N₂O) and ammonia (NH₃) emissions. The objectives of this study are to determine the effects of PCU on the relative nitrous oxide and ammonia loss to the atmosphere in a Kentucky bluegrass (Poa pratensis L.) field study using a photoacoustic gas analysis. Nitrogen was applied at 0, 10, 20, 30, and 40 Mg N ha^-1 and compared to uncoated and sulfur coated urea at 10 Mg N ha^-1.  Results equal or improved growth parameters, as well as significantly greater than anticipated decreases in emissions of both nitrous oxide and ammonia by using PCU. Ammonia losses peaked at 11 and 30 mg kg^-1 for PCU and urea, respectively. Average NH₃ losses were 4.6 and 8.7 mg kg^-1 for PCU and urea, respectively. Nitrous oxide losses peaked at 7 and 28 mg kg^-1 for PCU and urea, respectively. Average N₂O losses were 4.6 and 11.4 mg kg^-1 for PCU and urea, respectively. These results suggest that use of PCU has a tremendous potential to increase N use efficiency, resulting in significantly less emission of greenhouse gases.